1. Field of the Invention
This invention is directed to new catalysts of alkali fluorides and quaternary ammonium or phosphonium salts, to a process for their production and to their use as trimerization catalysts for the production of polyisocyanates containing isocyanurate groups.
2. Description of the Prior Art
Catalysts for the trimerization of organic isocyanates are known (J. H. Saunders and K. C. Frisch, Polyurethanes, Chemistry and Technology, pages 94 et seq. (1962)). Suitable trimerization catalysts are strong organic bases such as the alkali metal salts of carboxylic acids, metal alcoholates, metal phenolates, alkali metal carbonates, tertiary amines, tertiary phosphines and the "onium" compounds of nitrogen and phosphorus and also basic heterocycles of these elements
The use of quaternary ammonium hydroxides as catalysts for the trimerization of isocyanurate groups has often been o described. Thus, according to JP-PS No. 601 337 (U.S.Pat. No. 3,487,080), quaternary ammonium hydroxides are used together with certain co-catalysts. While the examples primarily illustrate the partial trimerization of aromatic diisocyanates, some examples illustrate the partial trimerization of aliphatic diisocyanates. However, the catalysts used for the trimerization of HDI in these examples result in predominantly cloudy products which are not suitable for coatings applications.
EP-A-10 589 is a further development of the Japanese patent specification cited above. According to this prior publication, quaternary ammonium hydroxides containing hydroxyalkyl substituents are used as catalysts for the trimerization of HDI. With these catalysts, HDI can be excellently trimerized to form products with no cloudiness. The disadvantage is that the hydroxyalkyl ammonium hydroxides are extremely difficult to produce in colorless form and have to be used in relatively large quantities of up to 0.6%. As a result, the end products of the process, i.e., the isocyanurate polyisocyanates freed from excess starting diisocyanate, may possibly show a yellowish coloration.
EP-A-47,452 describes the production of mixed trimers based on HDI and IPDI. Again, as can be seen from the examples, comparatively large quantities of catalysts are necessary.
Other known catalyst systems for the production of polyisocyanates containing isocyanurate groups also have serious disadvantages. For example, GB-PS No. 920,080, DE-OS No. 3,100,262, DE-OS No. 3,219,608 and DE-OS No. 3,240,613 describe the trimerization of HDI using metal-containing catalysts and co-catalysts such as phenols, alcohols or tertiary amines. The metal compounds can only be removed from the end products by elaborate processes, if at all, and can adversely affect subsequent applications and also the stability of the end products. In addition, the use of cocatalysts containing active hydrogen atoms leads to secondary reactions in which valuable isocyanate groups are consumed. The same also applies to EP-A-155,559, in which ammonium salts of organic acids are used as catalysts together with large amounts of alcoholic compounds.
EP-A-57,653, EP-A-89,297 and EP-A-187,105 describe organosilicon compounds which are used in comparatively large quantities. These compounds also cannot be completely removed from the end product and adversely affect its subsequent use.
Accordingly, an object of the present invention is to provide new catalysts for the partial trimerization of the isocyanurate groups of organic isocyanates which afford the following advantages.
The quantity of catalyst required is minimal. PA1 There is no need to use large quantities of cocatalysts. PA1 The new trimerization catalysts for the production of isocyanurate polyisocyanates result in colorless, noncloudy end products when colorless, noncloudy starting isocyanates are used.
It has now surprisingly been found that this object can be achieved by the catalyst systems described in detail hereinafter.